What Have We Learned About the Atmospheres of the Galilean

What have we learned about the atmospheres of the Galilean satellites of Jupiter?

A) None of these satellites has a permanent atmosphere.
B) Only Ganymede, the largest, has a permanent atmosphere of CO₂.
C) Callisto has a thin atmosphere of CO₂, whereas Ganymede has a thin atmosphere of O₂.
D) Ganymede and Callisto have thin atmospheres, whereas Io has a thick atmosphere of sulfur compounds.